Dennis D. Patton

Effect of noise correlation on detectability of disk signals in medical imaging

Pixel signal-to-noise ratio is one accepted measure of image quality for predicting observer performance in medical imaging. We have found, however, that images with equal pixel signal-to-noise ratio (SNRp) but different correlation properties give quite different observer-performance measures for a simple detection experiment. The SNR at the output of an ideal detector with the ability to prewhiten the noise is also a poor predictor of human performance for disk signals in high-pass noise. We have found constant observer efficiencies for humans relative to the performance of a nonprewhitening detector for this task.

Hemodynamic comparison of ventricular pacing, atrioventricular sequential pacing, and atrial synchronous ventricular pacing using radionuclide ventriculography

To assess the hemodynamic effects of physiologic pacing, 13 patients with DDD pacemakers who had varying degrees of atrioventricular (AV) block were studied with radionuclide ventriculography during VVI, DVI and VDD modes. Radionuclide ventriculography was performed with patient in the supine position at rest 5 to 10 minutes after the pacing mode and AV delay were changed. The AV delays selected were short (mean 147 +/- 4.8 ms) and long (mean 197 +/- 4.8 ms), with a constant difference of 50 ms. During VVI, 6 patients (group 1) had a left ventricular ejection fraction of 40% or less (mean 22 +/- 11) and 7 patients (group 2) had an ejection fraction of more than 40% (mean 59 +/- 11). Comparisons of ejection fraction, end-diastolic volume and cardiac index between VVI and both modes of AV pacing (VDD and DVI) and between long and short AV delays led to the following conclusions: DVI or VDD pacing produces more beneficial hemodynamic effects than VVI, and these effects are more pronounced in patients with low ejection fraction if longer AV delay is used. The VDD mode significantly improves ventricular function over the DVI mode in patients with an ejection fraction of more than 40% independent of heart rate. Longer AV delay is essential in patients with an ejection fraction of 40% or less to improve ventricular function with physiologic pacing.

FASTSPECT: electrical and mechanical design of a high-resolution dynamic SPECT imager

FASTSPECT is an imaging system designed for dynamic 3-D SPECT imaging of the brain. The system is based on 24 stationary modular cameras with a pinhole aperture structure having between 24 and 150 pinholes. Each camera is composed of 4 PMTs and a NaI(Tl) crystal. The original system has been replaced with a new gantry designed for use in a clinical environment. This opportunity was taken to add improved imaging capabilities. First, rotation of the aperture is now possible to acquire extra projections for static images. Second, high frame rates are obtainable by reducing dead-time between frames through distributed processing by assigning one Inmos T805 Transputer with 16 MB of RAM to each camera. Third, photomultiplier signals are now digitized to 8 bits instead of the previously used 5 bits. This additional ability allows different position-estimation schemes, including neural networks. The improved frame-rate capabilities have opened consideration of research in such areas as first-pass ventricular SPECT. Phantom studies have shown that sufficient counts can be collected in 1/20th second to reconstruct a full 3-D ventricular image. The new distributed electronics allows rapid data handling, so cardiac studies at 20 frames/sec are feasible.

A Utility-Based Model for Comparing the Cost-effectiveness of Diagnostic Studies

The effective cost of a diagnostic test is the money spent per unit of diagnostic performance. The latter can be measured as diagnostic utility (DU), the probability-weighted sum of the utilities of the four test outcomes TP, TN, FP, and FN: DU = U(TP)P(TP) + U(TN)P(TN) + U(FP)P(FP) + U(FN)P(FN). DU (which also is called expected utility) incorporates the clinical decision analytic variables sensitivity (Se), specificity (Sp), equivocal fraction (EF), disease probability (P(D)), and outcome utility (U). DU is not an inherent property of a diagnostic test but of test-observer interactions in a clinical setting. The model sets the effective cost (EC) of a diagnostic test = actual direct cost (ADC)/DU. When DU = 1 (perfect test) EC = ADC and the patient benefits from the test dollar for dollar. When DU less than 1, EC exceeds ADC. If DU approaches O, EC becomes infinite; the test has no effectiveness at any cost. DU depends strongly on P(D) if Se and Sp differ significantly; then EC also depends on P(D), and the effective cost of a test performed in the wrong P(D) setting may be several times its actual direct cost. This model of comparing effective costs compares actual direct cost with clinical measures of test performance and utility values that allow expression of patient/doctor fears and preferences. It offers a more clinically realistic setting than models based on costs alone.

Modular Scintillation Cameras: A Progress Report

Modular scintillation cameras are gamma cameras with relatively small crystal faces, a small number of photomultiplier tubes (PMTs), and independent processing electronics. Our prototypical module has a 10 cm square crystal face, four PMTs, and digital processing electronics. Scintillation event information is transferred to images by mapping digitized PMT response combinations to optimal position estimates of event locations. In our prototype, a look-up table is used to perform this mapping. To encode scintillation event information more effectively, we use nonlinear compression of each of the PMT signals. Also introduced are logarithmic matched filtering and likelihood windowing, two processing techniques that result from exploitations of the Poisson model of the distribution of photopeak events. Logarithmic matched filtering is a method of obtaining estimates of mean detector response functions having greater accuracy than that indicated by the digitization of the PMT responses. Likelihood windowing is the utilization of a likelihood threshold, rather than the familiar energy window, as a discriminant of photopeak and scatter events. We have implemented each of the above on our prototypical module. Performance characteristics of this module include energy resolution of 10% full width at half maximum (FWHM) at 140 keV and spatial resolution of better than 4mm FWHM over 90% of the crystal.

Predictive value of bone scans in an adjuvant breast cancer program

Technetium 99m phosphate‐complex bone scans were performed in 43 women within two months of mastectomy for stage I (1 patient), stage II (28 patients), and stage III (14 patients) breast cancer. Twelve (28%) initial bone scans were interpreted as either equivocally abnormal (6 scans) or definitely abnormal (6 scans). Radiographs confirmed metastatic disease in 2 patients who were then considered ineligible for adjuvant therapy (adriamycin‐cyclophosphamide with or without local radiotherapy). Of the remaining 41 eligible patients, all have received adjuvant therapy and 36 have had at least one additional bone scan at 6‐month intervals. Among 20 patients whose serial bone scans were unchanged, there has been no clinical recurrence with a mean followup of 20 months. In contrast, among 16 patients whose serial bone scans have changed (e.g., appearance of new focal lesions, disappearance of old lesions), there have been 6 clinical recurrences (p ρ 0.01) with a mean followup of 43 months. We conclude that carefully performed technetium pyrophosphate bone scans are helpful in the accurate initial staging of patients being considered for adjuvant breast cancer treatment, and that serial changes in the bone scan identify a group of patients at high risk for early recurrence.

Fractal Physiology And Nuclear Medicine Scans

Measurement of the power spectra of liver scans reveals that the radiocolloid distribution in the human liver behaves as a fractal object. Analysis of the power spectra suggests that the fractal dimension of the functional units of the liver changes with disease state, and that power spectral slope may be a useful classifier for the presence of disease. Models are proposed that relate the power spectral slope to the fractal dimension of the liver parenchyma.

Cobalt‐57 bleomycin for imaging head and neck tumors

Cobalt‐57 bleomycin imaging was performed in 11 patients with a history of head and neck cancer. Clinical and scan findings concurred on the presence and extent of tumor in 9 patients (82%); tumor was present in 7 and absent in 2 of the 9. In 2 patients (18%) the scan demonstrated tumor in the neck but failed to show metastatic sites. Cobalt‐57 bleomycin images were of good technical quality, with remarkably low background activity at 24 hours after administration. Cobalt‐57 bleomycin imaging appears to be a promising technique for evaluating patients with head and neck tumors.

Applications of Statistical Decision Theory in Nuclear Medicine

Over the last several years, Bayesian decision and estimation theory has become a central theme in the nuclear medicine research program at the University of Arizona. We have used concepts from this theory for image reconstruction, evaluation and optimization of imaging systems, position arithmetic in scintillation cameras, and in decision making in the operating room. In this paper, a brief review of Bayesian theory is given, followed by a survey of all of these applications, with emphasis on points of commonality among them.

Clinical value of the thallium-201 stress test sensitivity and specificity in the detection of coronary artery disease☆

Abstract Rest and exercise thallium-201 scintigraphy (201Tl stress test), 90% submaximal treadmill exercise test (ECG stress test), and coronary angiography were performed on 49 patients with suspected coronary artery disease. When technically unsatisfactory and uninterpretable scintiphotos were excluded, the sensitivity (true positives/true positives + false negatives) of the 201Tl stress test in detecting coronary artery stenosis ≥70% was 81%. The sensitivity of the 201Tl stress test in detecting coronary artery stenosis ≥50% was 84&‰ However, when technically unsatisfactory and uninterpretable studies were considered as failures of the test to detect disease, the sensitivity of the 201Tl stress test in detecting coronary artery stenosis ≥50% was 71%. The sensitivity of the ECG stress test was 92% in detecting stenosis ≥70% and 85%. in detecting stenosis ≥50% when non-diagnostic tests were excluded. However, when 11 non-diagnostic ECG stress tests were considered as a failure of the test to detect disease, the sensitivity of the ECG stress test in detecting coronary artery stenosis ≥50% was 64%. The sensitivity of the combined stress test in detecting coronary artery stenosis ≥50% was high whether or not technically unsatisfactory and uninterpretable studies were (89%) or were not (94%) included in the analysis. The specificity (true negatives,/true negatives + false positives) for ≥50% coronary artery stenosis was 90% for the 201Tl stress test, 75% for the ECG stress test and 80% for the combined stress test. Combined ECG and 201Tl stress testing detects a number of patients with significant coronary artery disease missed by ECG stress testing alone, primarily in those cases where the ECG stress test is non-diagnostic.